We present new results on the kinematics and spatial distribution of metal-enriched gas within {approx}125 kpc of star-forming ('Lyman break') galaxies at redshifts 2 {approx_lt} z {approx_lt} 3. In ...particular, we focus on constraints provided by the rest-frame far-ultraviolet (far-UV) spectra of faint galaxies, and demonstrate how galaxy spectra can be used to obtain key spatial and spectral information more efficiently than possible with QSO sightlines. Using a sample of 89 galaxies with (z) = 2.3 {+-} 0.3 and with both rest-frame far-UV and H{alpha} spectra, we re-calibrate the measurement of accurate galaxy systemic redshifts using only survey-quality rest-UV spectra. We use the velocity-calibrated sample to investigate the kinematics of the galaxy-scale outflows via the strong interstellar (IS) absorption lines and Ly{alpha} emission (when present), as well as their dependence on other physical properties of the galaxies. We construct a sample of 512 close (1''-15'') angular pairs of z {approx} 2-3 galaxies with redshift differences indicating a lack of physical association. Sightlines to the background galaxies provide new information on the spatial distribution of circumgalactic gas surrounding the foreground galaxies. The close pairs sample galactocentric impact parameters 3-125 kpc (physical) at (z) = 2.2, providing for the first time a robust map of cool gas as a function of galactocentric distance for a well-characterized population of galaxies. We propose a simple model of circumgalactic gas that simultaneously matches the kinematics, depth, and profile shape of IS absorption and Ly{alpha} emission lines, as well as the observed variation of absorption line strength (H I and several metallic species) versus galactocentric impact parameter. Within the model, cool gas is distributed symmetrically around every galaxy, accelerating radially outward with v{sub out}(r) increasing with r (i.e., the highest velocities are located at the largest galactocentric distances r). The inferred radial dependence of the covering fraction of cool gas (which modulates the absorption line strength) is f{sub c} (r) {proportional_to} r {sup -{gamma}} with 0.2 {approx_lt} {gamma} {approx_lt} 0.6 depending on transition. We discuss the results of the observations in the context of 'cold accretion', in which cool gas is accreting via filamentary streams directly onto the central regions of galaxies. At present, we find little observational evidence for cool infalling material, while evidence supporting the large-scale effects of superwind outflows is strong. This 'pilot' study using faint galaxy spectra demonstrates the potential of using galaxies to trace baryons within galaxies, in the circumgalactic medium, and ultimately throughout the intergalactic medium.
We present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey of the distant universe designed to explore the details of the connection between galaxies and ...intergalactic baryons within the same survey volumes, focusing particularly on scales from ~50 kpc to a few Mpc. The KBSS is optimized for the redshift range z ~ 2-3, combining S/N ~100 Keck/HIRES spectra of 15 of the brightest QSOs in the sky at z Asymptotically = to 2.5-2.9 with very densely sampled galaxy redshift surveys within a few arcmin of each QSO sightline. In this paper, we present quantitative results on the distribution, column density, kinematics, and absorber line widths of neutral hydrogen (H I) surrounding a subset of 886 KBSS star-forming galaxies with 2.0 <, ~ z <, ~ 2.8 and with projected distances < or =, slant3 physical Mpc from a QSO sightline. Using Voigt profile decompositions of the full Ly alpha forest region of all 15 QSO spectra, we compiled a catalog of ~6000 individual absorbers in the redshift range of interest, with 12 < or =, slant log (N sub(H i)) < or =, slant21. These are used to measure H I absorption statistics near the redshifts of foreground galaxies as a function of projected galactocentric distance from the QSO sightline and for randomly chosen locations in the intergalactic medium (IGM) within the survey volume. We find that N sub(H I) and the multiplicity of velocity-associated H I components increase rapidly with decreasing galactocentric impact parameter and as the systemic redshift of the galaxy is approached. The strongest H I absorbers within Asymptotically = to 100 physical kpc of galaxies have N sub(H I) ~3 orders of magnitude higher than those near random locations in the IGM. The circumgalactic zone of most significantly enhanced H I absorption is found within transverse distances of <, ~ 300 kpc and within + or -300 km s super(-1) of galaxy systemic redshifts. Taking this region as the defining bounds of the circumgalactic medium (CGM), nearly half of absorbers with log(N sub(H I)) > 15.5 are found within the CGM of galaxies meeting our photometric selection criteria, while their CGM occupy only 1.5% of the cosmic volume. The spatial covering fraction, multiplicity of absorption components, and characteristic N sub(H I) remain significantly elevated to transverse distances of ~2 physical Mpc from galaxies in our sample. Absorbers with N sub(H I) >10 super(14.5) cm super(-2) are tightly correlated with the positions of galaxies, while absorbers with lower N sub(H I) are correlated with galaxy positions only on >, ~Mpc scales. Redshift anisotropies on these larger scales indicate coherent infall toward galaxy locations, while on scales of ~100 physical kpc peculiar velocities of Delta v Asymptotically = to + or -260 km s super(-1) with respect to the galaxies are indicated. The median Doppler widths of individual absorbers within 1-3 r sub(vir) of galaxies are larger by Asymptotically = to 50% than randomly chosen absorbers of the same N sub(H I), suggesting higher gas temperatures and/or increased turbulence likely caused by some combination of accretion shocks and galactic winds around galaxies with M sub(halo) Asymptotically = to 10 super(12) M sub(middot in circle) at z ~ 2-3.
We present the first spectroscopic measurements of the shape of the far-ultraviolet (far-UV; lambda = 950-1500 A) dust attenuation curve at high redshift (z~ 3). Our analysis employs rest-frame UV ...spectra of 933 galaxies at z~ 3, 121 of which have very deep spectroscopic observations (> ~7 hr) at lambda = 850-1300 A, with the Low Resolution Imaging Spectrograph on the Keck Telescope. By using an iterative approach in which we calculate the ratios of composite spectra in different bins of continuum color excess, E(B- V), we derive a dust curve that implies a lower attenuation in the far-UV for a given E(B- V) than those obtained with standard attenuation curves. We demonstrate that the UV composite spectra of z~ 3 galaxies can be modeled well by assuming our new attenuation curve, a high covering fraction of H I, and absorption from the Lyman-Werner bands of H sub(2) with a small (< ~20%) covering fraction. The low covering fraction of H sub(2) relative to that of the H sub(1) and dust suggests that most of the dust in the ISM of typical galaxies at z~ 3 is unrelated to the catalysis of H sub(2), and is associated with other phases of the ISM (i.e., the ionized and neutral gas). The far-UV dust curve implies a factor of thickapproximate2 lower dust attenuation of Lyman continuum (ionizing) photons relative to those inferred from the most commonly assumed attenuation curves for L* galaxies at z~ 3. Our results may be utilized to assess the degree to which ionizing photons are attenuated in H II regions or, more generally, in the ionized or low column density (N(H I) < ~ 10 super(17,2) cm super(-2)) neutral ISM of high-redshift galaxies.
Using a large sample of spectroscopically confirmed z~ 3 galaxies, we establish an empirical relationship between reddening (E(B- V)), neutral gas covering fraction (f sub(cov)(H I)), and the escape ...of ionizing (Lyman continuum, LyC) photons. Our sample includes 933 galaxies at z~ 3, 121 of which have deep spectroscopic observations (> ~7 hr) at 850 < ~ lambda sub(rest)< ~ 1300 A with the Low Resolution Imaging Spectrograph on Keck. The high covering fraction of outflowing optically thick H i indicated by the composite spectra of these galaxies implies that photoelectric absorption, rather than dust attenuation, dominates the depletion of LyC photons. By modeling the composite spectra as the combination of an unattenuated stellar spectrum including nebular continuum emission with one that is absorbed by H 1 and reddened by a line-of-sight extinction, we derive an empirical relationship between E(B- V) and f sub(cov)(H 1). Galaxies with redder UV continua have larger covering fractions of H 1 characterized by higher line-of-sight extinctions. We develop a model which connects the ionizing escape fraction with E(B- V), and which may be used to estimate the ionizing escape fraction for an ensemble of galaxies. Alternatively, direct measurements of the escape fraction for our sample allow us to constrain the intrinsic LyC-to-UV flux density ratio to be left angle bracket S(900 A)/S(1500 A)right angle bracket sub(int)> ~ 0.20, a value that favors stellar population models that include weaker stellar winds, a flatter initial mass function, and/or binary evolution. Last, we demonstrate how the framework discussed here may be used to assess the pathways by which ionizing radiation escapes from high-redshift galaxies.
We present observations of Q1549-C25, an ~L* star-forming galaxy at z= 3.15 for which Lyman-continuum (LyC) radiation is significantly detected in deep Keck/LRIS spectroscopy. We find no evidence of ...contamination from a lower-redshift interloper close to the line of sight in the high signal-to-noise spectrum of Q1549-C25. Furthermore, the morphology of Q1549-C25 in V sub(606), J sub(125), and H sub(160)Hubble Space Telescope(HST) imaging reveals that the object consists of a single, isolated component within 1''. In combination, these data indicate Q1549-C25 as a clean spectroscopic detection of LyC radiation, only the second such object discovered to date at z~ 3. We model the spectral energy distribution of Q1549-C25, finding evidence of negligible dust extinction, an age (assuming continuous star formation) of ~1 Gyr, and a stellar mass of Mlow * = 7.9 x 10 super(9)Mmiddot in circle. Although it is not possible to derive strong constraints on the absolute escape fraction of LyC emission, f sub(esc)(LyC), from a single object, we use simulations of intergalactic and circumgalactic absorption to infer f sub(esc)(LyC) > or =, slanted 0.51 at 95% confidence. The combination of deep Keck/LRIS spectroscopy and Hubble Space Telescope imaging is required to assemble a larger sample of objects like Q1549-C25, and obtain robust constraints on the average f sub(esc)(LyC) at z~ 3 and beyond.
The evolution of the quasar luminosity function (QLF) is one of the basic cosmological measures providing insight into structure formation and mass assembly in the universe. We have conducted a ...spectroscopic survey to find faint quasars (-26.0 < M{sub 1450} < -22.0) at redshifts z = 3.8-5.2 in order to measure the faint end of the QLF at these early times. Using available optical imaging data from portions of the NOAO Deep Wide-Field Survey and the Deep Lens Survey, we have color-selected quasar candidates in a total area of 3.76 deg{sup 2}. Thirty candidates have R <= 23 mag. We conducted spectroscopic follow-up for 28 of our candidates and found 23 QSOs, 21 of which are reported here for the first time, in the 3.74 < z < 5.06 redshift range. We estimate our survey completeness through detailed Monte Carlo simulations and derive the first measurement of the density of quasars in this magnitude and redshift interval. We find that the binned luminosity function (LF) is somewhat affected by the K-correction used to compute the rest-frame absolute magnitude at 1450 A. Considering only our R <= 23 sample, the best-fit single power law (PHI {proportional_to} L {sup beta}) gives a faint-end slope beta = -1.6 +- 0.2. If we consider our larger, but highly incomplete sample going 1 mag fainter, we measure a steeper faint-end slope -2 < beta < -2.5. In all cases, we consistently find faint-end slopes that are steeper than expected based on measurements at z {approx} 3. We combine our sample with bright quasars from the Sloan Digital Sky Survey to derive parameters for a double-power-law LF. Our best fit finds a bright-end slope, alpha = -2.4 +- 0.2, and faint-end slope, beta = -2.3 +- 0.2, without a well-constrained break luminosity. This is effectively a single power law, with beta = -2.7 +- 0.1. We use these results to place limits on the amount of ultraviolet radiation produced by quasars and find that quasars are able to ionize the intergalactic medium at these redshifts.
Abstract
We present results of a deep spectroscopic survey quantifying the statistics of the escape of ionizing radiation from star-forming galaxies at
z
∼ 3. We measure the ratio of ionizing to ...non-ionizing UV flux density
, where
f
900
is the mean flux density evaluated over the range 880, 910 Å. We quantify the emergent ratio of ionizing to non-ionizing UV flux density by analyzing high signal-to-noise ratio composite spectra formed from subsamples with common observed properties and numbers sufficient to reduce the statistical uncertainty in the modeled IGM+CGM correction to obtain precise values of
, including a full-sample average
= 0.057 ± 0.006. We show that
increases monotonically with
, inducing an inverse correlation with UV luminosity as a by-product. We fit the composite spectra using stellar spectral synthesis together with models of the ISM in which a fraction
f
c
of the stellar continuum is covered by gas with column density
. We show that the composite spectra simultaneously constrain the intrinsic properties of the stars (
L
900
/
L
1500
)
int
along with
f
c
,
,
, and
f
esc,abs
, the absolute escape fraction of ionizing photons. We find a sample-averaged
f
esc,abs
= 0.09 ± 0.01, with subsamples falling along a linear relation
. Using the far-UV luminosity function, the distribution function
n
(
W
(Ly
α
)), and the relationship between
and
, we estimate the total ionizing emissivity of
z
∼ 3 star-forming galaxies with
M
uv
≤ −19.5, which exceeds the contribution of quasi-stellar objects by a factor of ∼3, and accounts for ∼50% of the total
ϵ
LyC
at
z
∼ 3 estimated using indirect methods.
We study the Ly alpha profiles of 36 spectroscopically detected Ly alpha -emitters (LAEs) at z ~ 2-3, using Keck MOSFIRE to measure systemic redshifts and velocity dispersions from rest-frame optical ...nebular emission lines. Thirty of the 36 Ly alpha emission lines are redshifted with respect to the systemic velocity with at least lsigma significance, and the velocity offset with respect to systemic Delta v sub(Ly) alpha is correlated with the R-band magnitude, M sub(UV), and the velocity dispersion measured from nebular emission lines with >3sigma significance: brighter galaxies with larger velocity dispersions tend to have larger values of Delta v sub(Ly) alpha . Our results are consistent with a scenario in which the Ly alpha profile is determined primarily by the properties of the gas near the systemic redshift; in such a scenario, the opacity to Ly alpha photons in lower mass galaxies may be reduced if large gaseous disks have not yet developed and if the gas is ionized by the harder spectrum of young, low metallicity stars.
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